Method and system for estimating operation parameters of a servomotor

ABSTRACT

A method for estimating operation parameters of a servomotor is described. The method includes the steps of: driving the servomotor to rotate stably at an initial angular velocity; computing d- and q-axis components of an initial voltage when the servomotor rotates at the initial angular velocity; accelerating the servomotor to a predetermined angular velocity according to the initial voltage; and computing at least one operation parameter of the servomotor after the servomotor rotates at the predetermined angular velocity.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Chinese Patent Application No.201510500888.X, filed on Aug. 14, 2015.

FIELD

The disclosure relates to a method and a system for estimating operationparameters of a servomotor, and more particularly to a method and asystem for estimating a torque constant, inertia and a frictioncoefficient of the servomotor.

BACKGROUND

Servomotor systems are widely used in industries, and a reliableautomatic control method of the servomotor system is needed, such thatmanpower cost may be reduced and productivity may be increased.

However, differently structured servomotors require different operationparameters (e.g., a torque constant, inertia and a friction coefficient)for control thereof.

SUMMARY

Therefore, an object of the disclosure is to provide a method and asystem for rapidly estimating operation parameters of a servomotor.

According to an aspect of the disclosure, the method for estimatingoperation parameters of a servomotor is described. The method is to beimplemented by a system that includes a current control loop foroutputting an output current to the servomotor, and a control module forcontrolling the current control loop. The method includes the followingsteps:

a) outputting, by the control module, a current signal to the currentcontrol loop to enable the current control loop to output the outputcurrent to the servomotor;

b) driving, by the current control loop, the servomotor to rotate stablyat an initial angular velocity by limiting integrated value of adifference between a current value of the current signal and a currentvalue of the output current;

c) computing, by the control module, d- and q-axis components of aninitial voltage when the servomotor rotates at the initial angularvelocity;

d) outputting, by the control module, the initial voltage having the d-and q-axis components to the current control loop for accelerating theservomotor from the initial angular velocity to a predetermined angularvelocity by feed-forward control; and

e) after the servomotor rotates at the predetermined angular velocity,computing, by the control module, at least one operation parameter ofthe servomotor.

According to another aspect of the disclosure, the system for estimatingoperation parameters of a servomotor includes a current control loop anda control module.

The current control loop is configured to output an output current tothe servomotor.

The control module is configured to control the current control loop,and is operable to:

output a current signal to the current control loop to enable thecurrent control loop to output the output current to the servomotor andto drive the servomotor to rotate stably at an initial angular velocityby limiting integrated value of a difference between a current value ofthe current signal and a current value of the output current;

compute d- and q-axis components of an initial voltage when theservomotor rotates at the initial angular velocity;

output the d- and q-axis components of the initial voltage to thecurrent control loop for accelerating the servomotor from the initialangular velocity to a predetermined angular velocity by feed-forwardcontrol; and

compute at least one operation parameter of the servomotor after theservomotor rotates at the predetermined angular velocity.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiments with reference tothe accompanying drawings, of which:

FIG. 1 is a block diagram illustrating an embodiment of system forestimating operation parameters of a servomotor according to thedisclosure;

FIG. 2 is a block diagram illustrating an embodiment of an angularposition control loop of the system according to the disclosure;

FIG. 3 is a block diagram illustrating an embodiment of a rotating speedcontrol loop of the system according to the disclosure;

FIG. 4 is a block diagram illustrating an embodiment of a currentcontrol loop of the system according to the disclosure;

FIG. 5 is a timing diagram for illustrating timing waveforms of acurrent signal used to control the current control loop, an outputcurrent outputted to the servomotor, and an angular velocity of theservomotor;

FIG. 6 is an enlarged plot for illustrating the timing waveform of theangular velocity;

FIG. 7 is a flow chart of a method for estimating the operationparameters of the servomotor according to the disclosure; and

FIG. 8 is a plot for illustrating a result of an experiment according toanother embodiment for computing an estimated torque constant, anestimated friction coefficient and an estimated inertia based upon theangular velocity.

DETAILED DESCRIPTION

Referring to FIG. 1, an embodiment of a system 100 for estimatingoperation parameters of a servomotor 4 according to this disclosure isillustrated. The servomotor 4 is connected to a load 2, and the system100 is configured to estimate the operation parameters of the servomotor4 for controlling the servomotor 4 to stably drive the load 2. In thisembodiment, the servomotor 4 is a permanent-magnet synchronous motor.

The system 100 includes a control loop module 3 and a control module 1.

The control loop module 3 includes a current control loop 32, a rotatingspeed control loop 31 and an angular position control loop 30. Thecurrent control loop 32 is configured to output an output current to theservomotor 4. The rotating speed control loop 31 is configured to drivethe servomotor 4 according to an angular velocity signal. The angularposition control loop 30 is configured to generate the angular velocitysignal outputted to the rotating speed control loop 31.

The control module 1 is configured to control the current control loop32 and the rotating speed control loop 31. In this embodiment, thecontrol module 1 is a computer provided with a software and/or afirmware. The control module 1 is programmed to cooperate with thecontrol loop module 3 to implement a method for estimating the operationparameters of the servomotor 4 according to this disclosure, so that theservomotor 4 loaded with the load 2 can be controlled, for example bythe control loop module 3, according to the operation parameters.

Referring further to FIG. 5, in durations t₀-t₇, the system 100 isconfigured to compute the operation parameters, such as an estimatedtorque constant {circumflex over (K)}_(t), an estimated inertia Ĵ and anestimated friction coefficient {circumflex over (B)}, of the servomotor4 loaded with the load 2. By tuning the control loop module 3 with theoperation parameters, the servomotor 4 can be controlled by the controlloop module 3 to stably operate.

It should be noted that, for the sake of convenience of description,notation standard are briefly addressed herein. A symbol with a “*”represents a value of an instruction signal, e.g., ω* represents anangular velocity value of the angular velocity signal for instructingthe rotating speed control loop 31. A symbol with a “̂” represents anestimated quantity, e.g., Ĵ represents the estimated inertia. A symbolwithout any tag represents an actual physical quantity, e.g., Ĵrepresents an actual inertia.

Block diagrams of the angular position control loop 30, the rotatingspeed control loop 31 and the current control loop 32 are illustrated inFIG. 2, FIG. 3 and FIG. 4, respectively.

Referring to FIG. 2, a transfer function of the angular position controlloop 30 is, but is not limited to,

${\frac{\theta (s)}{\theta^{*}(s)} = \frac{K_{p\_ p}}{s + K_{p\_ p}}},$

where θ is an angle value of an angular position of the servomotor 4, θ*is an angle value of an angle signal for instructing the angularposition control loop 30, K_(p) _(_) _(p) is a proportional gain of theangular position control loop 30 associated with a cutoff frequency anda bandwidth of the angular position control loop 30, and s is a complexfrequency parameter.

Referring to FIG. 3, a transfer function of the rotating speed controlloop 31 is, but is not limited to,

${\frac{\omega (s)}{\omega^{*}(s)} = {\frac{\frac{K_{i\_ v}}{B}}{s + \frac{K_{i\_ v}}{B}} = \frac{\omega_{v}}{s + \omega_{v}}}},$

where ω is an angular velocity value of an actual angular velocity ofthe servomotor 4, ω* is an angular velocity value of the angularvelocity signal, K_(i) _(_) _(ν) is an integral gain of the rotatingspeed control loop 31, B is an actual friction coefficient of theservomotor 4, and ω_(ν) is a bandwidth of the rotating speed controlloop 31 associated with the cutoff frequency.

In this embodiment, the rotating speed control loop 31 is implemented bya proportional integral controller (PI controller). The rotating speedcontrol loop 31 computes a difference by subtracting the angularvelocity value of the actual angular velocity ω of the servomotor 4 fromthe angular velocity value of the angular velocity signal ω*, which isgenerated by the angle control loop 30. Then, the rotating speed controlloop 31 processes the difference with reference to the integral gainK_(i) _(_) _(ν) and a proportional gain K_(p) _(_) _(ν) of the rotatingspeed control loop 31 so as to obtain a torque value of a torque signalT*_(e). It should be noted that values of the integral gain K_(i) _(_)_(ν) and the proportional gain K_(p) _(_) _(ν) are to be solved herein.Next, the torque value of the torque signal T*_(e) is divided by theestimated torque constant {circumflex over (K)}_(t) to obtain a currentvalue of a current signal i*. In particular, the current signal is usedto instruct the current control loop 32, and has a d-axis componenti*_(d) and a q-axis component i*_(q). Referring to FIG. 4, the currentcontrol loop 32 includes a q-axis control loop 321 and a d-axis controlloop 322. A transfer function of the q-axis control loop 321 is, but isnot limited to,

${\frac{i_{q}(s)}{i_{q}^{*}(s)} = {\frac{\frac{K_{p{\_ iq}}}{L_{q}}}{s + \frac{K_{p\_ iq}}{L_{q}}} = \frac{\omega_{iq}}{s + \omega_{iq}}}},$

where i_(q) is a q-axis component of the output current, i*_(q) is theq-axis component of the current signal, K_(p) _(_) _(iq) is aproportional gain of the q-axis control loop 321, L_(q) is a q-axisinductance, and ω_(iq) is a bandwidth of the q-axis control loop 321.The d-axis control loop 322 has a transfer function similar to that ofthe q-axis control loop 322. As shown in FIG. 4, i_(d) is a d-axiscomponent of the output current, i*_(d) is the d-axis component of thecurrent signal, K_(p) _(_) _(id) is a proportional gain of the d-axiscontrol loop 322, L_(d) is a d-axis inductance, and ω_(id) is abandwidth of the d-axis control loop 322.

Referring to FIG. 4 in combination with FIG. 3, since an output of thecurrent control loop 32 varies much faster than an output of therotating speed control loop 31, in this embodiment, the transferfunction of the q-axis control loop 321 of the current control loop 32is approximated by one, which means that the q-axis component of thecurrent signal i*_(q) is approximately equal to the q-axis componenti_(q) of the output current

$\left( {{i.e.},{\frac{i_{q}}{i_{q}^{*}} \approx 1}} \right).$

It is known that an actual motor torque T_(e) of the servomotor 4 isequal to the q-axis component i_(q) of the output current multiplied bya torque constant K_(t). The angular velocity value of the actualangular velocity ω of the servomotor 4 is derived from a differencebetween the actual motor torque T_(e) of the servomotor 4 and an actualload torque T_(L) of the load 2 with reference to the actual inertia Jand an actual friction coefficient B.

As illustrated in FIG. 4, in the q-axis control loop 321, a differencebetween the q-axis component i*_(q) of the current signal and the q-axiscomponent i_(q) of the output current that is fedback to an input of theq-axis control loop 321 is processed with reference to the proportionalgain K_(p) _(_) _(iq) and an integral gain K_(i) _(_) _(iq) of theq-axis control loop 321, and then combined with a q-axis componentν_(q0) of an initial voltage, so as to obtain a q-axis component ν_(q)of an output voltage outputted to the servomotor 4. Similarly, in thed-axis control loop 322, a difference between the d-axis componenti*_(d) of the current signal and the d-axis component i_(d) of theoutput current that is fedback to an input of the d-axis control loop322 is processed with reference to the proportional gain K_(p) _(_)_(id) and an integral gain K_(i) _(_) _(id) of the d-axis control loop322, and then combined with a d-axis component ν_(d0) of the initialvoltage, so as to obtain a d-axis component ν_(d) of the output voltage.

Furthermore, for the current control loop 32 in this embodiment,integrated values of the differences between the q- and d-axiscomponents i*_(q), i*_(d) of the current signal and the q- and d-axiscomponents i_(q), i_(d) of the output current are limited by respectivelimiters 3211, 3221 so as to limit the integrated values in a reasonablerange.

It is worth noting that the d-axis component i*_(d) is set as zero(i*_(d)=0) in this embodiment. In other words, only the q-axis componenti*_(q) of the current signal is considered in the following description,and the d-axis control loop 322 may be omitted in other embodiments.

Specifically, referring back to FIG. 1, the control module 1 includes acurrent configuring unit 11, an initial-voltage configuring unit 12, atorque-constant estimating unit 13, an initial-inertia estimating unit14, a friction-coefficient estimating unit 15, an inertia estimatingunit 16, a first calculator 171 and a second calculator 172.

At first, the current configuring unit 11 generates the q-axis componenti*_(q) of the current signal for the current control loop 32, and thecurrent control loop 32 drives the servomotor 4 to rotate stably at aninitial angular velocity ω₀ by limiting the integrated value of thedifference between the current value of the current signal i* and acurrent value of the output current.

When the servomotor 4 rotates at the initial angular velocity ω₀, theinitial-voltage configuring unit 12 of the control module 1 computes thed-axis component ν_(d0) and the q-axis component ν_(q0) of the initialvoltage, and outputs the d- and q-axis components ν_(d0), ν_(q0) of theinitial voltage to the current control loop 32 for accelerating theservomotor 4 from the initial angular velocity ω₀ to a predeterminedangular velocity ω₁ by feed-forward control and by relaxing thelimitation of the integrated value. The control module 1 then computesat least one operation parameter of the servomotor 4 after theservomotor 4 rotates at the predetermined angular velocity ω₁.

For example, when the servomotor 4 rotates at the predetermined angularvelocity ω₁, the torque-constant estimating unit 13 computes an initialestimated torque constant {circumflex over (K)}_(t0). Theinitial-inertia estimating unit 14 computes an initial estimated inertiaĴ₀ with the q-axis component i*_(q) of the current signal equal to zero(i.e., i*_(q)=0). The first calculator 171 computes an initialproportional gain K_(p) _(_) _(ν0) and an initial integral gain K_(i)_(_) _(ν0) of the rotating speed control loop 31 based upon the initialestimated torque constant {circumflex over (K)}_(t0) and the initialestimated inertia Ĵ₀, and then controls the rotating speed control loop31 with the initial proportional gain K_(p) _(_) _(ν0) and the initialintegral gain K_(i) _(_) _(ν0).

In addition, the control module 1 measures the q-axis component i_(q) ofthe output current which corresponds to the predetermined angularvelocity ω₁. Based upon the predetermined angular velocity ω₁ and theq-axis component i_(q) of the output current, the torque-constantestimating unit 13 computes the estimated torque constant {circumflexover (K)}_(t), and the friction-coefficient estimating unit 15 computesthe estimated friction coefficient {circumflex over (B)}. Furthermore,the inertia estimating unit 16 computes the estimated inertia Ĵ usingcurve fitting based upon a plurality of angular velocity values and theestimated friction coefficient {circumflex over (B)}.

Finally, the second calculator 172 computes a proportional gain K_(p)_(_) _(ν) and an integral gain K_(i) _(_) _(ν) for controlling therotating speed control loop 31 based upon the estimated torque constant{circumflex over (K)}_(t) and the estimated friction coefficient{circumflex over (B)}.

Referring to FIGS. 1 and 5-7, the method implemented by the system 100for estimating the operation parameters of the servomotor 4 has thefollowing steps. It should be noted again that the d-axis componenti*_(d) of the current signal is set as zero (i*_(d)=0) throughout theprocedure of this embodiment.

In duration t₀-t₁ (step S1), the current configuring unit 11 of thecontrol module 1 outputs the q-axis component i*_(q) of the currentsignal to the current control loop 32 to enable the current control loop32 to output the q-axis component i_(q) of the output current to theservomotor 4. In step S1, the q-axis component i*_(q) of the currentsignal is equal to i₁ (i*_(q)=i₁).

The current control loop 32 drives the servomotor 4 to rotate stably atthe initial angular velocity ω₀ by limiting the integrated value of thedifference between the q-axis component i*_(q) of the current signal andthe q-axis component i_(q) of the output current. When the servomotor 4reaches the initial angular velocity ω₀ at instant t₁, the q-axiscomponent i_(q) of the output current is equal to i₂ (i₁=i₂).

In duration t₁-t₂ (step S2), the initial-voltage configuring unit 12computes d- and q-axis components ν_(d0) and ν_(q0) of the initialvoltage when the servomotor 4 rotates at the initial angular velocityω₀. The d- and q-axis components ν_(d0) and ν_(q0) of the initialvoltage is computed based upon:

ν_(d0)=−ω₀ ×P×L _(q) ×i _(q), and

ν_(q0)=ω₀ ×P×L _(d) ×i _(d)+ω₀ ×P×λ,

where L_(d) and L_(q) are respectively d- and q-axis components ofinductance, P are pole pair of servomotor, and λ is a physical quantityof flux linkage. Reference may be made to “Permanent Magnet Synchronousand Brushless DC Motor Drives,” 2010 (Ch. 3, pages 227-233) forcalculation of the physical quantity of the flux linkage.

In duration t₂-t₃ (step S3), the initial-voltage configuring unit 12outputs the initial voltage having the d- and q-axis components ν_(d0)and ν_(q0) to the current control loop 32, so that the servomotor 4 isaccelerated by feed-forward control. As a result, the q-axis componenti_(q) of the output current follows the q-axis component i*_(q) of thecurrent signal. When the q-axis component i_(q) of the output currentreaches the q-axis component i*_(q) of the current signal, the controlmodule 1 commands the current control loop 32 to relax the limitation ofthe integrated value, so as to accelerate the servomotor 4 to achievethe predetermined angular velocity ω₁ at instant t₃.

In duration t₃-t₄ (step S4), the servomotor 4 stably rotates at thepredetermined angular velocity ω₁, and the torque-constant estimatingunit 13 computes the initial estimated torque constant {circumflex over(K)}_(t0) based upon

${{\hat{K}}_{t\; 0} = {\frac{3}{2} \cdot \frac{v_{q}}{\omega}}},$

where ω is the angular velocity value of the actual angular velocity ofthe servomotor 4. In the following, the initial-inertia estimating unit14 computes the initial estimated inertia Ĵ₀ based upon

${{\hat{J}}_{0} = \frac{{\hat{K}}_{t\; 0} \times i_{1}}{\alpha}},$

where α is a current angular acceleration of the servomotor 4accelerating from the initial angular velocity ω₀ to the predeterminedangular velocity ω₁, and i₁ is the value at which the q-axis componenti*_(q) of the current signal is set (i*_(q)=i₁). Next, the currentconfiguring unit 11 outputs to the current control loop 32 the currentsignal with the q-axis component i*_(q) equal to zero (i*_(q)=0), sothat the rotating speed control loop 31 takes over the controlling ofthe servomotor 4 from the current control loop 32.

Then, the first calculator 171 computes the initial proportional gainK_(p) _(_) _(ν0) based upon K_(p) _(_) _(ν0)=2·ω_(ν)·J₀ and the initialintegral gain K_(i) _(_) _(ν0) based upon K_(i) _(_) _(ν0)=ω_(ν) ²·J₀.Following the computation of the initial proportional gain K_(p) _(_)_(ν0) and the initial integral gain K_(i) _(_) _(ν0), the control module1 controls the rotating speed control loop 31 with the initialproportional gain K_(p) _(_) _(ν0) and the initial integral gain K_(i)_(_) _(ν0). It is worth noting that in FIG. 5, the angular velocityvalue of the actual angular velocity ω of the servomotor 4 decreasesslightly at the beginning of the duration t₃-t₄. The decrease of theangular velocity value of the actual angular velocity ω is attributed tothe q-axis component i*_(q) of the current signal being forced to zero(i*_(q)=0) when the rotating speed control loop 31 takes over control ofthe servomotor 4 from the current control loop 32. However, the angularvelocity value of the actual angular velocity ω recovers eventually tothe predetermined angular velocity ω₁ after the rotating speed controlloop 31 controls the servomotor 4 with the initial proportional gainK_(p) _(_) _(ν0) and the initial integral gain K_(i) _(_) _(ν0).

Furthermore, at the end of the duration t₃-t₄ (step S5), thetorque-constant estimating unit 13 computes the estimated torqueconstant {circumflex over (K)}_(t) of the servomotor 4 based upon

${{\hat{K}}_{t} = {1.5 \times \frac{v_{q} - {i_{3} \cdot r_{s}}}{\omega_{1}}}},$

and the friction-coefficient estimating unit 15 computes the estimatedfriction coefficient {circumflex over (B)} of the servomotor 4 basedupon

${\hat{B} = \frac{{\hat{K}}_{t} \cdot i_{3}}{\omega_{1}}},$

where r_(s) is a resistance value of the servomotor 4, and i₃ is theq-axis component i_(q) of the output current measured when theservomotor rotates 4 at the predetermined angular velocity ω₁ in theduration t₃-t₄.

Finally, in duration t₄-t₇ (step S6), the control module 1 deactivatesthe servomotor 4 so as to make the servomotor 4 decelerate for computingthe estimated inertia Ĵ. Referring to FIG. 6, when the servomotor 4decelerates to an angular velocity value ω₂ between ω₁ and ω₀, theinertia estimating unit 16 samples a plurality of angular velocityvalues ω_(d1) to ω_(dn) during deceleration of the servomotor 4, i.e.,in duration t₅-t₆, and computes the estimated inertia Ĵ using curvefitting.

Specifically, the estimated inertia Ĵ is computed based upon

${\hat{J} = \frac{\hat{B}}{N}},$

where N is a constant associated with time solved by the curve fittingwith an exponential function ω(t)=M·e^(N-t), and M is a constantassociated with the angular velocity of the servomotor 4 solved by thecurve fitting with the exponential function.

Subsequently, the second calculator 172 computes the proportional gainbased upon K_(p) _(_) _(ν)=ω_(ν)·Ĵ and the integral gain based uponK_(i) _(_) _(ν)=ω_(ν)·{circumflex over (B)}, and controls the rotatingspeed control loop 31 with the proportional gain K_(p) _(_) _(ν) and theintegral gain K_(i) _(_) _(ν). Therefore, the rotating speed controlloop 31 is capable of controlling the servomotor 4 to stably operate.

Referring to FIG. 8, a result of an experiment according to anotherembodiment is illustrated. The result shows that, by the method of thisdisclosure, the estimated torque constant is computed as

${\hat{K}}_{t} = {4.78 \times 10^{- 1}\left( \frac{N \cdot m}{A} \right)}$

during acceleration of the servomotor 4, the initial estimated inertiais computed as Ĵ₀=1.4×10⁻³ (kg·m²) when the servomotor 4 rotatessubstantially at 1500 rpm, the estimated friction coefficient iscomputed as

$\hat{B} = {2.45 \times 10^{- 3}\left( \frac{N \cdot m}{{rad}\text{/}\sec} \right)}$

during deceleration of the servomotor 4, and the estimated inertia iscomputed as Ĵ=3.44×10⁻⁴ (kg·m²) before the servomotor 4 comes to a stop.The duration for estimating the operation parameters by the method ofthis disclosure is only about 1.4 seconds.

Referring to Table 1 below, an error between each of the operationparameters estimated by the method of this disclosure and manual settingvalue is shown. The error of the estimated inertia Ĵ is 5.0%. The errorof the estimated friction coefficient {circumflex over (B)} is roughly5.1%. The error of the estimated torque constant {circumflex over(K)}_(t) is roughly 1.5%.

TABLE 1 Manual setting value Estimation Error Inertia 3.28 × 10⁻⁴ 3.44 ×10⁴ 5.0% (kg · m²) $\begin{matrix}{Friction} \\{coefficient} \\\left( \frac{N \cdot m}{{rad}/\sec} \right)\end{matrix}\quad$ 2.33 × 10⁻³ 2.45 × 10⁻³ 5.1% $\begin{matrix}{Torque} \\{constant} \\\left( \frac{N \cdot m}{A} \right)\end{matrix}\quad$ 4.86 × 10⁻¹ 4.78 × 10⁻¹ 1.5%

By the method of this disclosure, the system 100 is capable ofestimating the operation parameters of the servomotor 4 and computingthe proportional gain K_(p) _(_) _(ν) and the integral gain K_(i) _(_)_(ν) according to the operation parameters for automatically controllingthe servomotor 4 within about 1.4 seconds.

To sum up, by limiting the integrated value of the difference betweenthe current value of the current signal i* and the current value of theoutput current, operation errors of the servomotor 4 are reduced so thatthe servomotor 4 controlled by the system 100 is capable of stableoperation. Moreover, by the method of this disclosure, the operationparameters, such as the estimated inertia Ĵ, the estimated frictioncoefficient {circumflex over (B)} and the estimated torque constant{circumflex over (K)}_(t), are automatically, precisely and rapidlycomputed during operation of the servomotor 4. So-called dynamicperformance, i.e. automatically and rapidly tuning the operationparameters for control of the servomotor 4, is achieved.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiment. It will be apparent, however, to oneskilled in the art, that one or more other embodiments may be practicedwithout some of these specific details. It should also be appreciatedthat reference throughout this specification to “one embodiment,” “anembodiment,” an embodiment with an indication of an ordinal number andso forth means that a particular feature, structure, or characteristicmay be included in the practice of the disclosure. It should be furtherappreciated that in the description, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure and aiding in theunderstanding of various inventive aspects.

While the disclosure has been described in connection with what isconsidered the exemplary embodiment, it is understood that thisdisclosure is not limited to the disclosed embodiment but is intended tocover various arrangements included within the spirit and scope of thebroadest interpretation so as to encompass all such modifications andequivalent arrangements.

What is claimed is:
 1. A method for estimating operation parameters of aservomotor, the method to be implemented by a system that includes acurrent control loop for outputting an output current to the servomotor,and a control module for controlling the current control loop, themethod comprising the steps of: a) outputting, by the control module, acurrent signal to the current control loop to enable the current controlloop to output the output current to the servomotor; b) driving, by thecurrent control loop, the servomotor to rotate stably at an initialangular velocity by limiting integrated value of a difference between acurrent value of the current signal and a current value of the outputcurrent; c) computing, by the control module, d- and q-axis componentsof an initial voltage when the servomotor rotates at the initial angularvelocity; d) outputting, by the control module, the initial voltagehaving the d- and q-axis components to the current control loop foraccelerating the servomotor from the initial angular velocity to apredetermined angular velocity by feed-forward control; and e) after theservomotor rotates at the predetermined angular velocity, computing, bythe control module, at least one operation parameter of the servomotor.2. The method of claim 1, the system further including a rotating speedcontrol loop that is controlled by the control module to drive theservomotor according to an angular velocity signal, wherein, in step c),the control module is configured to compute the d- and q-axis componentsof the initial voltage based upon:ν_(d0)=−ω₀ ×P×L _(q) ×i _(q), andν_(q0)=ω₀ ×P×L _(d) ×i _(d)+ω₀ ×P×λ, where ν_(d0) and ν_(q0) arerespectively the d- and q-axis components of the initial voltage, L_(d)and L_(q) are respectively d- and q-axis components of inductance, ω₀ isthe initial angular velocity, P are pole pair of servomotor, i_(d) andi_(q) are respectively d- and q-axis components of the output current,and λ is a physical quantity of flux linkage; wherein, in step d), thecontrol module outputs the initial voltage to the current control loop,so that the q-axis component of the output current follows a q-axiscomponent of the current signal.
 3. The method of claim 2, wherein: instep d), when the q-axis component of the output current reaches theq-axis component of the current signal, the control module commands thecurrent control loop to relax the limitation of the integrated value, soas to accelerate the servomotor to achieve the predetermined angularvelocity; in step e), the control module computes an estimated frictioncoefficient when the servomotor rotates at the predetermined angularvelocity.
 4. The method of claim 3, wherein step e) includes thesub-steps of: when the servomotor rotates at the predetermined angularvelocity ω₁, computing an initial estimated torque constant based upon${{\hat{K}}_{t\; 0} = {\frac{3}{2} \cdot \frac{v_{q}}{\omega}}},$where ν_(q) is a q-axis component of an output voltage outputted to theservomotor, and ω is an actual angular velocity of the servomotor;outputting to the current control loop the current signal with theq-axis component thereof equal to zero, and computing an initialestimated inertia based upon${{\hat{J}}_{0} = \frac{{\hat{K}}_{t\; 0} \times i_{1}}{\alpha}},$where α is a current angular acceleration of the servomotor, and i₁ is avalue at which the q-axis component of the current signal is set;computing an initial proportional gain based upon K_(p) _(_)_(ν0)=2·ω_(ν)·Ĵ₀ and an initial integral gain based upon K_(i) _(_)_(ν0)=ω_(ν) ²·Ĵ₀; and controlling the rotating speed control loop withthe initial proportional gain K_(p) _(_) _(ν0) and the initial integralgain K_(i) _(_) _(ν0).
 5. The method of claim 4, wherein step e) furtherincludes the sub-steps of: deactivating the servomotor so as to make theservomotor decelerate; sampling a plurality of angular velocity valuesduring deceleration of the servomotor; and computing an estimatedinertia using curve fitting based on the angular velocity values and theestimated friction coefficient.
 6. The method of claim 5, wherein, instep e), the control module is configured to compute an estimated torqueconstant {circumflex over (K)}_(t) based upon${\hat{K}}_{t} = {1.5 \times \frac{v_{q} - {i_{3} \cdot r_{s}}}{\omega_{1}}}$and the estimated friction coefficient {circumflex over (B)} based upon$\hat{B} = \frac{{\hat{K}}_{t} \cdot i_{3}}{\omega_{1}}$ when theservomotor rotates at the predetermined angular velocity, where r_(s) isa resistance value of the servomotor, and i₃ is a q-axis component ofthe output current corresponding to the predetermined angular velocityω₁; wherein the control module is configured to compute the estimatedinertia Ĵ based upon ${\hat{J} = \frac{\hat{B}}{N}},$ where N is aconstant associated with time solved by the curve fitting with anexponential function ω(t)=M·e^(N-t), and M is a constant associated withthe angular velocity of the servomotor solved by the curve fitting withthe exponential function.
 7. The method of claim 6, further comprisingthe steps of computing a proportional gain based upon K_(p) _(_)_(ν)=ω_(ν)·Ĵ and an integral gain based upon K_(i) _(_)_(ν)=ω_(ν)·{circumflex over (B)}, and controlling the rotating speedcontrol loop with the proportional gain K_(p) _(_) _(ν) and the integralgain K_(i) _(_) _(ν).
 8. A system for estimating operation parameters ofa servomotor, the system comprising: a current control loop configuredto output an output current to the servomotor; and a control moduleconfigured to control said current control loop, and being operable tooutput a current signal to said current control loop to enable saidcurrent control loop to output the output current to the servomotor andto drive the servomotor to rotate stably at an initial angular velocityby limiting integrated value of a difference between a current value ofthe current signal and a current value of the output current, compute d-and q-axis components of an initial voltage when the servomotor rotatesat the initial angular velocity, output the d- and q-axis components ofthe initial voltage to said current control loop for accelerating theservomotor from the initial angular velocity to a predetermined angularvelocity by feed-forward control, and compute at least one operationparameter of the servomotor after the servomotor rotates at thepredetermined angular velocity.
 9. The system of claim 8, furthercomprising a rotating speed control loop configured to be controlled bysaid control module to drive the servomotor according to rotating speedof the servomotor, wherein said control module is configured to computethe d- and q-axis components of the initial voltage based upon:ν_(d0)=−ω₀ ×P×L _(q) ×i _(q), andν_(q0)=ω₀ ×P×L _(d) ×i _(d)+ω₀ ×P×λ, where ν_(d0) and ν_(q0) arerespectively the d- and q-axis components of the initial voltage, L_(d)and L_(q) are respectively d- and q-axis components of inductance, ω₀ isthe initial angular velocity, P are pole pair of servomotor, i_(d) andi_(q) are respectively d- and q-axis components of the output current,and λ is a physical quantity of flux linkage; wherein said currentcontrol loop is configured to output the output current having theq-axis component that follows a q-axis component of the current signal.10. The system of claim 9, wherein said control module includes afriction-coefficient estimating unit configured to: when the q-axiscomponent of the output current reaches the q-axis component of thecurrent signal, command said current control loop to re lax thelimitation of the integrated value, so as to accelerate the servomotorto achieve the predetermined angular velocity; and compute an estimatedfriction coefficient when the servomotor rotates at the predeterminedangular velocity.
 11. The system of claim 10, wherein said controlmodule includes: a current configuring unit configured to output to saidcurrent control loop the current signal with the q-axis component equalto 0; a torque-constant estimating unit configured to compute an initialestimated torque constant when the servomotor rotates at thepredetermined angular velocity; an initial-inertia estimating unitconfigured to compute an initial inertia based on the initial estimatedtorque constant when the servomotor rotates at the predetermined angularvelocity; and a calculator configured to compute an initial proportionalgain and an initial integral gain based on the initial inertia, and tocontrol said rotating speed control loop with the initial proportionalgain and the initial integral gain.
 12. The system of claim 11, wherein:said torque-constant estimating unit is configured to compute theinitial estimated torque constant based upon${{\hat{K}}_{t\; 0} = {\frac{3}{2} \cdot \frac{v_{q}}{\omega}}},$where ν_(q) is a q-axis component of an output voltage outputted to theservomotor, and ω is a current angular velocity of the servomotor; saidinitial-inertia estimating unit is configured to compute the initialinertia based upon${{\hat{J}}_{0} = \frac{{\hat{K}}_{t\; 0} \times i_{1}}{\alpha}},$where α is a current angular acceleration of the servomotor, and i₁ is avalue at which the q-axis component of the current signal is set; andsaid calculator is configured to compute the initial proportional gainbased upon K_(p) _(_) _(ν0)=2·ω_(ν)·Ĵ₀ and to compute the initialintegral gain based upon K_(i) _(_) _(ν0)=ω_(ν) ²·Ĵ₀.
 13. The system ofclaim 11, wherein said control module further includes an inertiaestimating unit configured to: deactivate the servomotor so as to makethe servomotor decelerate; sample a plurality of angular velocity valuesduring deceleration of the servomotor; and compute an estimated inertiausing curve fitting based on the angular velocity values and theestimated friction coefficient.
 14. The system of claim 13, wherein saidcontrol module is further operable to: compute an estimated torqueconstant {circumflex over (K)}_(t) based upon${\hat{K}}_{t} = {1.5 \times \frac{v_{q} - {i_{3} \cdot r_{s}}}{\omega_{1}}}$and the estimated friction coefficient {circumflex over (B)} based upon$\hat{B} = \frac{{\hat{K}}_{t} \cdot i_{3}}{\omega_{1}}$ when theservomotor rotates at the predetermined angular velocity, where r_(s) isa resistance value of the servomotor, and i₃ is a q-axis component ofthe output current corresponding to the predetermined angular velocityω₁; and compute the estimated inertia Ĵ based upon${\hat{J} = \frac{\hat{B}}{N}},$ where N is a constant associated withtime solved by the curve fitting with an exponential functionω(t)=M·e^(N-t), and M is a constant associated with the angular velocityof the servomotor solved by the curve fitting with the exponentialfunction.
 15. The system of claim 14, wherein said control module isfurther operable to compute a proportional gain based upon the estimatedinertia, to compute an integral gain based upon the estimated frictioncoefficient, and to control said rotating speed control loop with theproportional gain and the integral gain.
 16. The system of claim 15,wherein said control module is operable to compute the proportional gainbased upon K_(p) _(_) _(ν)=ω_(ν)·Ĵ, and to compute the integral gainbased upon K_(i) _(_) _(ν)=ω_(ν)·{circumflex over (B)}.